1. Field of the Invention
This invention relates generally to bonding methods for use with materials such as glass, quartz, metal, ceramic and the like. More specifically, the invention relates to a method for bonding ring laser gyroscope mirrors to bodies of ring laser gyroscopes.
2. Description of Related Art
In one common form of compact ring laser gyroscope, a block comprising a glass, quartz, ceramic or similar material and having a low coefficient of thermal expansion (CTE) forms the body of the gyroscope. A number of components, typically composed of glass or metal, such as electrodes, mirrors, and readout apparatus, are attached to the gyroscope body. Sealed passages in the body allow communication among the various components. The passages of the gyroscope body are filled with a lasing gas that lases when current is applied to the gyroscope.
A cathode and two anode components are used to apply current; they are designed to create beams of laser light that travel in opposite directions through the gyroscope body. The cathode and anodes may be composed of aluminum, steel, nickel or other metals that meet the design requirements for the gyroscope. The other components attached to the gyroscope may be glass mirrors, or may be glass/metal assemblies that, for instance, allow adjustment of gyroscope mirror position to improve gyroscope performance.
The life and accuracy of the gyroscope is largely affected by the ability of the components to be properly bonded to the gyroscope body in such a way as to prevent escape of lasing gas or contamination of the gyroscope passages with foreign gasses. In an ideal case, the seal should be hermetic, meaning that a negligible amount of gas is exchanged between the passages in the gyroscope body and the atmosphere during the life of the gyroscope. Thus, the method used to seal the components to the gyroscope body is critical to the performance of the gyroscope.
The bonding method may also affect the operating range of the gyroscope, depending on the conditions under which the bonding materials degrade. Of particular concern are bonding materials having melting temperatures that limit the possible applications of the gyroscope (i.e. oil drilling, high speed/altitude aircraft, etc.). As another consideration, the bonding process and materials should not interfere with or alter previously completed processing steps, nor limit subsequent processing steps.
With these considerations in mind, numerous methods of bonding the components to the gyroscope body have been used, each with some measure of success. High-temperature epoxy, for example, has been used as an effective material for glass-to-glass bonds. Indium or other soft metals have been popular for glass-to-metal bonds. Both epoxy and indium have been effective in part because they are flexible enough to compensate for the differences in the CTE of the two materials being bonded. Other bonding methods, such as graded bonds and the use of glass frits, which attempt to match the CTE of the two materials to be bonded together, have also been successful.
Unfortunately, the epoxy and soft metal bonding techniques, due to the flexibility of the bond materials, tend to allow outgassing or fail to provide a bond capable of withstanding the pressures typically required for high-end gyroscopes. Indium, in particular, extrudes out of the bonding area with repeated use of the device, eventually causing failure of the gyroscope. Neither epoxy nor soft metal allow the gyroscope to be operated at high temperatures, since the limit of a gyroscope""s range of operation is the melting temperature of the bonding material. In some cases, an even lower limit results if the bonding material begins to degrade below its melting temperature. These same factors will also affect the types of processing the gyroscope can withstand subsequent to formation of the bond.
Glass flits, which are used for bonding two identical materials or materials with nearly identical CTEs, require less cleaning and preparation of the bonding surfaces than required when forming indium seals. The use of glass frits is known to produce consistent and inexpensive hermetic seals. Unfortunately, the glass frit bonding process requires an elevated temperature which substantially limits the types of processing which can be done near the area of the bond prior to the bonding process. Furthermore, there is an inverse relationship between frit bonding temperature and the CTE for the frits used; frits with low CTEs (near those of typical gyroscope body materials) have such high processing temperatures that they exceed the thermal limits of the gyroscope body. Thus, use of frits usually introduces a thermal mismatch into the gyroscope since a compromise must be made between bonding temperature and the CTE of the frit.
Accordingly, a bonding method that can be implemented at relatively low temperature, that produces a high-temperature hermetic seal, and that requires less preparation, is needed.
In a first principal aspect, a method of attaching at least one component to a ring laser gyro block is disclosed. The method may comprise positioning the component so that a mounting surface of the at least one component is substantially parallel to a mounting surface of the ring laser gyro block and applying a fluid adhesive to the exposed interface of the mounting surface of the component and the mounting surface of the ring laser gyro block. Applying the fluid adhesive to the interface may cause it to wick into the interface. The method also includes allowing the fluid adhesive to harden. The fluid adhesive may be an aqueous silicate prepared using a sol-gel process, an aqueous sodium silicate, or another suitable adhesive.
In a second principle aspect, the method may further comprise establishing a gap of between about 0.0001 inches and about 0.015 inches between the mounting surface of the component and the mounting surface of the ring laser gyro block, wherein the fluid adhesive wicks into the gap.
In a third principle aspect, a ring laser gyro block assembly comprising a ring laser gyro block is disclosed, the assembly further comprising at least one component attached to the ring laser gyro block by a cured fluid adhesive. The component is attached by positioning it so that its mounting surface is substantially parallel to a mounting surface of the ring laser gyro block, and then applying a fluid adhesive to the interface of the mounting surface of the component and the mounting surface of the ring laser gyro block, wherein the fluid adhesive wicks between the mounting surfaces. The fluid adhesive is then allowed to harden.